heat pulse velocity sap flow sensors

Sap Flow Sensors

  • Equidistant, 3-needle design that can be used with various heat pulse velocity methods
  • Flexible approach to how you measure heat velocity in woody stems
  • Use our data logger algorithm or develop your own algorithm
  • Simple sturdy design allows for this sensor to be used for long periods for time
  • Includes both pre-written programs for data loggers and software to quick data analysis and interpretation
  • Sensors are manufactured by East 30 Sensors


low cost sensors to maximise research outcomes

The SF3 Sap Flow Sensors are low cost, highly accurate and reliable sensors for the measurement of sap flow, transpiration, and even stem water content, in plants.

The SF3 Sap Flow Sensors are ideally suited for scientific researchers interested in plant water use, physiology, or hydrology research. The sensors provide the greatest flexibility for scientists needing to undertake field work or research in the glasshouse.

The sensors connect directly to the Campbell Scientific range of data loggers and can be used in combination with other environmental sensors such as VPD, solar radiation, soil moisture, or water potential. Edaphic Scientific can supply data logging equipment for you, or we can assist you in connecting the sensors to your existing data logger network.

The SF3 Sap Flow Sensors are also unique in that stem water content can be measured simultaneously with sap flow or transpiration. Additional equipment is not required – stem water content can be measured with the same sensors that are measuring sap flow.


who is using the SF3 Sap Flow Sensor?

The SF3 sensor is currently being used by researchers, students and growers in many research projects around the globe. For example, researchers in Australia at the University of Queensland, the University of Melbourne and RMIT University currently use the SF3 sensors for their scientific studies. Around the globe, researchers at University of Florida, USA, and Helmholtz Centre Potsdam, Germany, are also using the SF3 sensors.

There have been many scientific publications citing the SF3 sensors. Some example publications are discussed further below on this webpage. In the past, scientists at Stanford University, University of California, Colorado State University, University of Arizona, University of Arkansas, USDA, University of Western Australia, Max-Plank Institute, ETH Zurich, University of Freiburg, Technical University of Munich, and many more have published research in international peer reviewed journals citing the SF3 Sap Flow Sensors.


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Tmax Sap Flow Sensorsensor design
  • Number of needles: 3 – downstream and upstream temperature needles and middle heater element needle;
  • Needle Length: 35 mm
  • Distance between needles: Equidistant, 6 mm spacing
  • Number of thermistors: 6 – 3 downstream thermistors and 3 upstream thermistors
  • Position of thermistors: 5 mm, 17.5 mm and 30 mm from tip of needle (called inner, middle and outer temp sensor positions, respectively – see figure to the right)


sensor specifications

Download Detailed SF3 Specification Sheet

feature specification
Measurement Principle Heat Pulse Velocity
Measurement Range -10 to +200 cm/hr heat velocity
Accuracy 0.2 cm/hr heat velocity
Resolution 0.0001 cm/hr heat velocity
Temperature Sensors 10K Precision Thermistor
Heater Resistance 44 ohms
Cable Length 5m (standard) | 20m maximum



Heat Ratio Methodaccessories needed
  • Heater control interface: One interface will run up to 4 sensors. 
  • Data Logger: Campbell Scientific CR1000 Data Logger – Edaphic Scientific can supply data loggers and program them for you
  • Recommended: Drilling guide for precise spacing of needles in the tree.


measurement theory

Edaphic Scientific has developed a heat pulse algorithm that builds on the heat pulse velocity research of Marshall (1958), Cohen et al (1981), Green et al (2003) and Pearsall et al (2014).

Our approach combines equations originally developed by Marshall (equation 15, 1958) and Cohen et al (1981, see equation 5 in Green et al 2003).

The following is Marshall’s equation 15:

slow rates of flow equation

Where V is heat velocity (cm/hr), k is thermal diffusivity, x1 is the distance between the temperature needles and heater needles, and v1 and v2 are the rise in temperature, from initial temperature, following a short heat pulse.

Marshall’s (1958) equation 15 was called the “slow rates of flow” method (SRFM). As the original title suggests, the method is only applicable for low, reverse and moderate rates of sap flow. Bleby et al (2008), Green et al (2008) and Pearsall et al (2014) confirmed this and suggested the maximum rate of flow that the SRFM can detect is around 35 to 40 cm/hr. However, many woody species record heat velocities greater than 40 cm/hr, and even as fast as 200 cm/hr.

The following is the Tmax equation (after equation 5 in Green et al 2003):

Tmax Sap Flow

Where Xd is the distance of the downstream temperature needle from the heater needle and tm is the time, in seconds, recorded until the maximum temperature rise following the heat pulse.

The Tmax method is able to resolve very fast heat velocities upwards of 200 cm/hr and beyond. The Tmax method, however, cannot accurately resolve heat velocity below 10 cm/hr.

In the Pearsall et al (2014) paper, they introduced a “dual heat pulse technique” that was a combination of the compensation heat pulse method (CHPM) and heat ratio method (HRM).

The Tmax and CHPM methods are similar in many respects with research of the CHPM technique having evolved from initial research on the Tmax technique.

However, the approach adopted by Pearsall et al (2014) has the disadvantage of having 2 sets of probes installed close to each other in the stem, or 4 needles in parallel at appropriate spacing. The additional needles in the stem can lead to increase variance and error in heat velocity measurements.

The algorithm Edaphic Scientific has developed simultaneously measures heat velocity via the SRFM and Tmax methods with a 3-needle sensor design.

By using our approach with the 3-needle sensor design, rather than the 4 or more needle design of Pearsall et al (2014), means less sources of error during installation and data collection, less sensors, lower costs, and the ability to connect more sensors to a single data logger (increase sample size).

As Pearsall et al (2014) showed, it is possible to switch between the two methods so that the SRFM is favoured at reverse, slow and moderate velocities (i.e. up to 35 to 40 cm/hr), and the Tmax method is favoured at high velocities (>40 cm/hr).

Once heat velocities are recorded by the data logger, correction factors, such as wounding and probe misalignment, as well as sapwood properties, such as moisture content, are included in a post-analysis of the data. From this analysis, sap velocity and volumetric sap flow can be determined by equations established in the literature.

Edaphic Scientific’s capabilities

At Edaphic Scientific we want to work with you from the start of your project through to its completion. We can provide:

  • Assistance with project and experimental design
  • Procurement of all monitoring equipment, including sensors, data loggers and data management software. Edaphic Scientific is a one-stop shop where we can source and find any necessary equipment for your project from our preferred suppliers or third party suppliers
  • Installation and training
  • On-going assistance with data interpretation and equipment maintenance
  • Data correction and analysis, including statistical analysis with the R-package
  • Report and publication preparation including tables, figures, graphs, and manuscript writing


advanced data collection and management solutions

DMS IPhoneEdaphic Scientific recognises the need for flexible and adaptable sensor and data logging solutions for experimental or environmental monitoring projects.

You can connect the HPV sap flow sensors to our data logging systems, or we can assist you in connecting the sap flow sensors to your existing system.

Data can be downloaded directly in the field from data loggers. Alternatively, data can be downloaded over the internet on your iPhone, iPad or desktop computer with the Eagle.io cloud-based, data management software solutions.

Edaphic Scientific provides sap flow sensors with:

Individual loggers or

Whole-System solutions with a centrally located data logger, multiplexers and additional equipment such as weather stations, soil moisture, water potential, carbon and nutrient monitoring.

Data can be collected directly from logging units with a USB download cable or remotely, anywhere in the world, via the mobile phone network and an internet connection.


individual data loggers

Data LoggersEdaphic Scientific supplies a one-to-one sap flow sensor to data logger monitoring solution.

The East 30 Sensors HPV sap flow sensors are compatible with Campbell Scientific’s CR300 data logger for a low cost, individual data logging solution.

Edaphic Scientific provides both the sap flow sensor and pre-programmed, pre-configured CR300 data logger. Power supply is via a solar panel and 12V battery, and the data loggers are stored in an environmentally sealed protective housing.

The individual sap flow data loggers are ideal for:

  • Urban tree monitoring: where security and safety for equipment is paramount. The data logger and power supply can be installed high and out of reach, or installed in underground pits. The cable for the sap flow sensors can be any length and sensors can be installed on any part of the tree trunk. If the sap flow sensors were damaged or vandalised, they can be quickly and cheaply replaced as they are low cost sensors.
  • Remote tree monitoring: in remote locations, it may not be practical to have a single, centrally located data logging system with cables extended to various trees for sap flow monitoring. The individual sap flow data loggers are ideal in such projects.
  • Horticulture and Viticulture: growers often require to run machinery and undertake other management procedures without worrying about tripping, cutting or damaging cabling and monitoring equipment. With a individual sap flow data logger, it is possible to undertake precision plant water use measurements on individual trees or vines without the need for extensive cabling and power supplies.


whole-system monitoring solutions

Weather StationEdaphic Scientific can supply multiple sap flow sensors all connected to a single, centrally located data logging system, with multiplexers, power supply and environmentally protective housing.

Additional parameters can be added to the system for the monitoring of meteorological variables, soil moisture, water potential and soil carbon concentration.

Edaphic Scientific can supply a monitoring system that is completely pre-programmed, pre-configured and ready to be installed. We can also provide assistance with field installation and training of staff and students.


free software

When you procure sap flow equipment through Edaphic Scientific, we will provide software to you free of charge.

Why do you need software for sap flow measurements?

The East 30 Sensors measure the velocity of a heat pulse in the sapwood of trees. Known as “heat velocity”, this parameter is useful for basic and initial interpretation of direction of sap movement as well as checking for probe misalignment and correct sensor installation.

But most researchers and managers are not interested in heat movement and really want to know how water, or sap, is moving in trees.

Therefore, the free software is required to convert the heat velocity values into sap velocity, sap flux and sap flow based on correction factors.

The free software can also be used to calculate total tree water use.


sap flow sensor installation
sap flow sensor drill guide

Sap flow sensor drill guide attached to a small stem with cable ties.

Sap flow sensors are relatively easy to install in trees – particularly with some practice. Edaphic Scientific can provide training for you on correct approach to sap flow sensor installation.

Along with your sap flow sensors, we provide additional items for sensor installation including drill guide, drill bits and grafting wax.

There is a standardised protocol for sap flow sensor installation and measurements provided on Prometheus Wiki, a website maintained by the CSIRO.

East 30 Sensors also provides a detailed manual that explains how to install sap flow sensors.




Sap Flow Sensorpublications

Bleby, T.M., et al. 2008. Limitations of the HRM: great at low flow rates, but no yet up to speed? In ‘7th International Workshop on Sap Flow: Book of Abstracts’. (International Society of Horticultural Sciences: Seville, Spain)

Cohen, Y., et al. 1981. Improvement of the heat pulse method for determining sap flow in trees. Plant, Cell and Environment 4:391-397.

Green, S., et al. 2003. Theory and practical application of heat pulse to measure sap flow. Agronomy Journal 95: 1371-1379.

Green, S., et al. 2008. A re-analysis of heat pulse theory across a wide range of sap flows. ISHS Acta Horticulturae 846: VII International Workshop on Sap Flow. DOI: 10.17660/ActaHortic.2009.846.8

Marshall, D.C. 1958. Measurement of sap flow in conifers by heat transport. Plant Physiology 33: 385-396.

Pearsall, K.R., et al 2014. Evaluating the potential of a novel dual heat-pulse sensor to measure volumetric water use in grapevines under a range of flow conditions. Functional Plant Biology 41: 874-883.